Finished lubricants consist of two general components; lubricating base oil and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to their properties. In general, a few lubricating base oils are used to manufacture a variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives.
Base oils are usually prepared from hydrocarbon feedstocks having a major portion boiling above 650° F. Typically, the feedstocks from which lubricating base oils are prepared are recovered as part of the bottoms from an atmospheric distillation unit. This high boiling bottoms material may be further fractionated in a vacuum distillation unit to yield cuts with pre-selected boiling ranges. Most lubricating base oils are prepared from that fraction or fractions where a major portion boils above about 700° F. (about 370° C.) and below about 1050° F. (about 565° C.). Although lubricating base oils traditionally have been prepared from conventional petroleum feedstocks, recently it has been shown that high quality lubricating base oils can be prepared from synthetic feedstocks such as polyalphaolefins (PAOs) and from waxy feedstocks, such as slack wax and Fischer-Tropsch wax.
Numerous governing organizations, including Original Equipment Manufacturers (OEM's), the American Petroleum Institute (API), Association des Consructeurs d'Automobiles (ACEA), the American Society of Testing and Materials (ASTM), International Lubricant Standardization and Approval Committee (ILSAC), and the Society of Automotive Engineers (SAE), among others, define the specifications for lubricating base oils and finished lubricants. Increasingly, the specifications for engine oils and other finished lubricants are calling for products with excellent low temperature properties, high oxidation stability, and low volatility. Currently, only a small fraction of the base oils manufactured today are able to meet these demanding specifications.
Oxidation stability is an important property of base oils intended for use in the formulation of finished lubricants, and means for improving the oxidation stability for both petroleum derived and synthetic base oils has been an active of area for research. The more resistant base oil is to oxidation, the fewer tendencies the finished lubricant will have to form deposits, sludge, and corrosive byproducts in the engine. Oxidation stability also helps prevent undesirable viscosity increases during use. One method for improving oxidation stability of base oils is by saturating the double bonds present in the molecules. For example, see U.S. patent application Ser. No. 09/343,334 which describes improving the oxidative stability of PAOs by hydrogenating to a very low Bromine Index (BI).
Bromine Index (ASTM 2710-99) is the standard analytical method for measuring unsaturation in petroleum hydrocarbons. The BI represents the number of milligrams of Bromine that react with 100 gms of the sample under the conditions of the test. However, many lubricating base oils have a boiling range above the level specified for measuring BI. In addition, many of the newer synthetic hydrocarbons have hindered olefins that are not measurable by BI. Hydrocarbons which contain hindered olefins, such as PAOs, poly internal olefins, or other oligomerized base oil, give erroneously low results with conventional BI analysis. Therefore, there is a need for a method for accurately measuring olefins in hydrocarbons having boiling points over a broad range, from about 500° F. (about 260° C.) to well above 1500° F. (about 816° C.).
NMR spectroscopy has been shown to be useful for characterizing base oils and predicting bulk properties such as viscosity index, aniline point, and pour point. For example, T. M. Shea, S. Gunsel, “Modeling Base Oil Properties using NMR Spectroscopy and Neural Networks”, Tribology Transactions, Vol. 45 (2003), pp. 296-302, teaches that 13C NMR may be used to measure the weight percent of aromatics and the weight percent of aliphatic carbons. See also “NMR Molecular Characterization of Lubricating Base oils: Correlation with Their Performance”, L. Montanari, C. Como and S. Fattori, Applied Magnetic Resonance, 14, (1998), pp. 345-356. V. Bansal et al., “Estimation of Bromine Number of Petroleum Distillates by NMR Spectroscopy”, Energy and Fuels, Vol. 14 (2000), pp. 1028-1031 describes the use of NMR in estimating the bromine numbers of fuel samples with boiling ranges from 50 to 250° C. (122 to 482° F.). However, the literature has not shown that NMR spectroscopy can be used to measure the weight percent of olefins present in high boiling hydrocarbons such as base oils. The present invention is based upon the discovery that 1H NMR may be used to accurately analyze for the amount of olefins present in a base oil and establish a target value which may be used to correlate with high oxidation stability.
As used in this disclosure the word “comprises” or “comprising” is intended as an open-ended transition meaning the inclusion of the named elements, but not necessarily excluding other unnamed elements. The phrase “consists essentially of” or “consisting essentially of” is intended to mean the exclusion of other elements of any essential significance to the composition. The phrase “consisting of” or “consists of” is intended as a transition meaning the exclusion of all but the recited elements with the exception of only minor traces of impurities.